We are investigating mechanisms by which different activities in the cell nucleus are connected to the transcription apparatus via interactions with the hyper-phosphorylated C-terminal repeat domain (PCTD) of elongating RNA polymerase II. Because differential phosphorylation of the CTD determines which proteins bind to it, we are characterizing the activities and chromosomal distribution of Ctk1-kinase, the principal elongation-phase CTD kinase in yeast. Excitingly, we just identified the Ctk1 functional counterparts in Drosophila and human cells as CDK12 and CDK13, and we are beginning intensive investigations of these metazoan Ctk1 kinases. We are also characterizing numerous factors that interact with Ctk1-generated forms of the PCTD (PCTD-associating proteins, or PCAPs). We recently discovered a novel set of CTD-associated DNA repair / recombination proteins and events (CARR proteins / events), and we have begun experiments delving into the components and mechanisms at play in this new area of investigation. To continue our investigations, we propose the following SPECIFIC AIMS: AIM 1: Analyze Ctk1-kinases and CTD Phosphorylation, from Yeast to Man. Many important features of CTD phosphorylation and function are poorly understood; our goal is to illuminate these features. Toward this end we have engineered constructs and developed approaches that will facilitate more in-depth analysis of yeast Ctk1-kinase (CTDK-I) and better evaluation of PCTD functions in RNA processing and chromatin remodeling. In addition, our demonstration that metazoan CDK12 and CDK13 are CTD kinases orthologous to yCTK1 enables us to extend our investigations into D. melanogaster and H. sapiens. Given the virtual absence of knowledge about these CTD kinases in animals, we foresee that our results will provide a host of novel insights into CTD phosphorylation and transcription elongation-related events in multicellular eukaryotes. AIM 2: Investigate CTD-Associated Repair & Recombination, from Yeast to Man. We will follow up vigorously our recent demonstration that PCTD-associating proteins play critical roles in responding to DNA damage and suppressing inappropriate recombination in transcribed genes. Because these insights are so new, there is only rudimentary knowledge about mechanisms and macromolecular components involved. To help fill this huge knowledge void, we will investigate Ctk1 kinase-dependent CARR inside of transcribed genes in yeast, fruit fly and man. These studies will delineate molecular players and mechanisms of PCTD- dependent responses to DNA damage, and they will provide insights into events and mechanisms of PCTD- dependent modulation of transcription-associated recombination. Because mutations affecting the human versions of CARR proteins can lead to human disease, including cancer, we know already that many of our insights will be medically relevant.